1. Field of the Invention
The present invention relates generally to the field of wireless communications, and particularly to the design of antennas with differential inputs and outputs.
2. Background
Certain wireless communications applications, such as those using Bluetooth and other ISM (Industrial Scientific and Medical) bands, use chipsets with differential inputs and outputs. Typically, antennas are only single-ended with a ground reference. When used together, the aforementioned antennas and chipsets are not fully compatible because the chipsets include a balanced line (one that has two conductors with equal currents in opposite directions) and the antennas an unbalanced line (one that has just one conductor and a ground).
To get around this incompatibility, baluns are often included in the design. A balun is a device that joins a balanced line to an unbalanced line. A balun is essentially a type of transformer that is used to convert an unbalanced signal to a balanced one or vice versa. Baluns isolate a transmission line and provide a balanced output.
In the case of multi-band applications, classical solutions are problematic because they require that multiple antennas be dedicated to meet the requirements of the targeted application. Especially in the case of mobile communications devices, where space is at a premium, this can be a serious hurdle to implementation. It can also be costly, because the construction of a balun is expensive, and can cost well more than the antenna itself—and at least several times the cost of capacitors.
The subject of this invention is an antenna with differential inputs and outputs that can be compatible with chipsets used in applications such as Bluetooth and ISM. Advantages of such a solution include efficiency, which is achieved by extraction of more gain from the chipset.